Rapid scalable fabrication of stable copper electrowetting valves

Abstract

Reliable and scalable micro-valves on flexible materials are attractive for fluid management and enhanced device functionality for disposable microfluidic applications. Here, a microfluidic electrowetting valve was fabricated on a poly(ethylene terephthalate) substrate based on the principle of electrowetting-on-dielectric. Copper electrodes were fabricated by inkjet-printing a copper oxide nanoparticle ink and rapidly reduced to conductive copper using intense pulsed light sintering. A hydrophilic and a hydrophobic electrode are required for low-voltage actuation of the valve. To produce the hydrophobic electrode, poly(perfluorooctyl methacrylate) was uniformly coated over the copper electrode via initiated chemical vapor deposition. Systematic experiments were performed to study the effect of dielectric layer thicknesses and applied voltages on the droplet contact angle. Electrodes with dielectric layers of 14, 38, and 92 nm were actuated at 2 V, and at the same applied voltage, the droplet contact angle decreased fastest for electrodes coated with the thinnest dielectric layers. Polymer-coated copper electrodes were demonstrated to remain stable throughout a 3-month aging study at ambient conditions and showed consistent wetting behavior at low voltages. Furthermore, a microfluidic device was fabricated using laser cut parts to demonstrate separate actuation of two electrowetting valves at an applied voltage of 3 V. These results offer compelling opportunities for integration of copper electrowetting valves into low-cost microfluidic devices using scalable techniques.

Graphical abstract